(1) Field of the Invention
The present invention relates generally to an apparatus for inspecting the interior of generally vertical conduits or piping and, more particularly, to an apparatus for detecting and determining both the axial and angular positions of detected defects in the variable diameter jet pump diffusers such as found in a boiling water (BWR) nuclear reactors.
(2) Description of the Prior Art
Coolant piping in a BWR must be periodically inspected to detect cracking due to either intergranular Stress Corrosion Cracking (IGSCC) or fatigue in the tubing walls, so that these areas can be repaired to prevent leakage. Usually detection is performed externally since there was no way to insert an inspection probe into the jet pump diffuser assembly consisting of the jet pump mixers, diffuser and adapters. This is because the access opening to the internal tubing is limited while the inside diameter of the piping may vary over its length from between about 3 to 22 inches. However, because of supports and other attachments, not every portion of the piping can be inspected externally.
Probes have been developed to detect and located defects inside the much smaller steam generator tubing which has an inside diameter of about 3/4 inch. These probes may include a rotatable probe head positioned at the end of a tubular carrier through which electrical wiring connects the drive means and detector of the probe head to an external power source and controls. The probe head includes a detector, e.g., an ultrasonic detector, an eddy current detector, or both, which measures changes in wall conditions.
The axial position of the wall defect can be determined by measuring the distance that the probe head has been inserted into the tubing. In addition, encoders have been used to determine the angular position of the defect which is helpful in properly correcting the defect. One example of such a probe for steam generator tubing is disclosed in U.S. Pat. No. 5,760,306 (to be issued Jun. 2, 1998), issued to Wyatt, III et al., which is hereby incorporated by reference in its entirety. However these probes could not be used for the much larger and variable diameter jet pump diffuser assembly piping which varies between about 3 and 22 inches over its length.
Thus, there remains a need for a new and improved apparatus for detecting and determining both the axial and angular positions of detected defects in the inside of a pipe while, at the same time, is able to conform to large, variable diameter jet pump diffusers such as found in a BWR nuclear reactors.